1. Field of the Invention
The present invention relates generally to explosive compositions of the type comprising a liquid explosive, an oxygen-supplying salt, and a carbonaceous absorbent, and more particularly to an explosive composition having an improved carbonaceous absorbent.
2. Description of the Prior Art
Dynamite is a blasting explosive that is made from a liquid explosive, typically nitroglycerin or ethylene glycol dinitrate (EGDN), absorbed in a porous material together with an oxygen-supplying salt. By adding a small amount of a nitrate ester of cellulose, gelatin dynamite or gelignite is formed. Such gelatin dynamites form a plasticized mass which is water resistant and capable of being formed into a desired shape. Semigelatin dynamites incorporate about one-half the nitrocellulose and less nitroglycerin than gelatin dynamites and have physical properties between dynamites and gelatin dynamites. Both dynamites and semigelatin dynamites may include a major portion of ammonium nitrate as a substitute explosive for the nitroglycerin.
The absorbent material in such formulations is typically a ground carbonaceous material of vegetable origin such as ground plant stalk, wood flour, sawdust, bagasse, and the like. Usually, such low-density absorbents are combined with less absorbent, but higher density, materials such as ivory nut and meal, apricot pit meal, and the like. The relative amounts of low-density and high-density carbonaceous materials may be balanced to provide an explosive having a desired density and explosive strength.
Formulations of the type just described are well-known in the art and suffer from certain common drawbacks. The amount of highly-absorbent low-density carbonaceous material that can be added is limited by the need to provide complete combustion of the carbonaceous material. Incomplete combustion leads to the formation of carbon monoxide which can be toxic when the explosive is used in an enclosed space, such as an underground mine. The limited amount of absorbent material leads to a less stable explosive which can exude the liquid explosive at high temperatures and/or after prolonged storage.
A second problem relates to gelatin dynamites, which are commonly used in seismographic oil exploration, which requires that they may be submerged in water at high pressure. The formulations must resist the incursion of water for periods extending up to ten or more days without desensitization to detonation by the blasting cap. The desensitization results from both the compression of microscopic air bubbles in the gelatin by the high hydrostatic pressure and the incursion of water into the explosive which dissolves the oxidizing salts reducing the loading density. Thus, while gelatin dynamite is typically considered waterproof, the cell cavities of the ground plant tissues which form the absorbent are vulnerable to penetration by water at high pressure. The result is the penetration of the cell cavities by water. The result is that the explosive becomes discontinuous with small accumulations of water held in individual cell cavities. Such a structure adversely affects the detonation-propagation characteristics of the explosive leading to a reduction of the detonation velocity and finally, incomplete or low-order detonation.
Thus, it would be desirable to provide an explosive composition which is stable and resists loss of the liquid explosive even at high temperatures, as well as being water-resistant even when held under high pressure for a number of days.
The use of various ground cellulose materials as an absorbent or fuel in an explosive composition is revealed in a number of prior patents. For example, U.S. Pat. No. 1,444,594 discloses the use of sawdust, ground bark and ground nut shells, each of which is primarily cellulose. Other patents reveal the use of ground plant stalks, moss and wood flour (U.S. Pat. No. 2,211,737); ground barley flour (U.S. Pat. No. 2,314,806); ground ivory nut meal, rice meal and linseed meal (U.S. Pat. No. 2,314,832); rye flour and flaked vegetable grains (U.S. Pat. No. 2,358,384); almond hull pulp (U.S. Pat. No. 1,880,116); bagasse, ground walnut hulls and apricot pits (U.S. Pat. No. 3,728,174); wheat flour (U.S. Pat. No. 3,881,970); and tamarind seed flour and guar (U.S. Pat. No. 4,233,095). Heretofore, the use of processed cellulose material in which the lignin has been removed and the cell wall broken has not been known in the prior art.
U.S. Pat. No. 3,728,174 also discloses the addition of hollow, resinous plastic spheres to a gelatin dynamite to provide extra air bubbles which are resistant to collapse at high pressure. Such "microballoons" do not prevent water incursion, however.